U.S. patent application number 11/921860 was filed with the patent office on 2009-09-03 for adjustable dental tool drive arrangement.
Invention is credited to Kevin John Bailey, Jean Castonguay, Andrew Douglas Millson, Derek M.J. Turner.
Application Number | 20090220911 11/921860 |
Document ID | / |
Family ID | 37498088 |
Filed Date | 2009-09-03 |
United States Patent
Application |
20090220911 |
Kind Code |
A1 |
Bailey; Kevin John ; et
al. |
September 3, 2009 |
Adjustable dental tool drive arrangement
Abstract
The invention relates to an improved dental tool drive
arrangement for a hand-piece with a drive head, the tool drive
arrangement permitting length adjustment of the tool in the drive
head by concentrically supporting the tool in the drive head at any
position from a fully inserted position to a maximum retracted
position. The tool drive arrangement preferably includes a tool and
a rotatable tool supporting element for concentrically supporting
the tool from the fully inserted to the maximum retracted position,
the tool preferably including a maximum retraction indicator for
indicating to a user when the tool has been retracted to the
maximum retraction position. This provides a significant advantage
over the prior art by allowing a user to adjust the exposed length
of a rotatable tool, preferably a dental bur, without exceeding
safe operating limits. The invention also relates to an improved
drive spindle which allows depth adjustment of a tool in a dental
handpiece while maintaining efficient torque transfer and
concentricity during high speed rotation.
Inventors: |
Bailey; Kevin John; (Ottawa,
CA) ; Millson; Andrew Douglas; (Ottawa, CA) ;
Turner; Derek M.J.; (Ottawa, CA) ; Castonguay;
Jean; (Hudson, CA) |
Correspondence
Address: |
Diederiks & Whitelaw
12471 Dillingham Sq #301
Woodbridge
VA
22192
US
|
Family ID: |
37498088 |
Appl. No.: |
11/921860 |
Filed: |
June 9, 2006 |
PCT Filed: |
June 9, 2006 |
PCT NO: |
PCT/CA2006/000954 |
371 Date: |
April 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60689052 |
Jun 10, 2005 |
|
|
|
Current U.S.
Class: |
433/126 |
Current CPC
Class: |
A61B 17/162 20130101;
A61C 1/144 20130101; A61C 1/145 20130101; A61C 1/141 20130101; B23B
31/005 20130101; B25G 1/005 20130101; B23B 2260/0487 20130101; A61C
3/02 20130101 |
Class at
Publication: |
433/126 |
International
Class: |
A61C 1/00 20060101
A61C001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 1, 2005 |
US |
11262959 |
Claims
1-52. (canceled)
53. A rotatable tool drive assembly for use with a dental or
medical handpiece having a drive head with an axis of rotation, the
assembly comprising: a rotatable tool; and a tool drive arrangement
for releasably supporting the tool, the tool drive arrangement
being insertable into the drive head for coaxial rotation in the
drive head; the tool having a tool body with an axis of rotation, a
driven portion with a driven end for insertion into the tool drive
arrangement and a working portion for projecting from the drive
head during use; the tool drive arrangement having a tool passage
for coaxially receiving the driven portion of the tool at different
insertion depths, the tool passage including a first tool seat for
concentrically supporting the driven end of the tool and a second
tool seat for concentrically supporting the driven portion of the
tool at a location intermediate the driven end and the working
portion; the first tool seat being axially elongated for
concentrically supporting the driven end at any position from a
maximum insertion depth wherein the drive end is fully inserted
into the tool passage to a maximum retraction depth wherein the
tool is retracted from the maximum insertion depth and the drive
end is still engaged in the first tool seat.
54. The rotatable tool drive assembly of claim 53, wherein the tool
includes a maximum retraction indicator for indicating to a user
when the tool has been retracted to the maximum retraction
depth.
55. The rotatable tool drive assembly of claim 54, wherein the tool
drive arrangement includes a drive spindle for being fittingly
received in a drive spindle socket of the drive head, the drive
spindle having a drive torque receiving portion for receiving drive
torque from the drive head, a tool supporting portion connected
with the drive torque receiving portion and having the tool passage
with first and second tool seats, the drive spindle further
including a tool retaining member for releasably retaining the
driven portion in the tool passage; and the axial length of the
first tool seat being selected for the tool retaining member to
engage the driven portion at any position of the tool from the
maximum insertion position to the maximum retraction position.
56. A rotatable dental tool for use in a tool drive arrangement
having a tool passage for coaxially receiving the tool and
including first and second tool seats for concentrically supporting
the tool, the first tool seat being axially elongated for
concentrically supporting the tool at different insertion depths,
the tool comprising: a tool body having an axis of rotation, the
tool body divided into a driven portion with a driven end for
insertion into the tool passage of the tool drive arrangement and a
working portion with a working end for projection from the tool
drive arrangement during use; and a maximum retraction indicator on
the driven portion for indicating to a user when the tool is
retracted from the supporting portion to a maximum retraction depth
wherein the drive end is only partially inserted in the first tool
seat.
57. The tool of claim 56, wherein the maximum retraction indicator
is a mechanical indicia located on the driven portion for
engagement by a portion of the tool supporting element when the
maximum retraction depth is reached.
58. The tool of claim 57, wherein the mechanical indicia is a stop
on the driven portion for mechanical interaction with the
supporting element when the tool is retracted to the maximum
retraction depth.
59. The tool of claim 56, for use in an air turbine driven
handpiece.
60. The tool of claim 59, wherein the tool is a dental bur.
61. The rotatable tool drive assembly according to claim 53,
wherein the tool drive arrangement is a drive spindle comprising: a
torque receiving element for receiving rotational torque from the
drive; a tool supporting element connected with the torque
receiving element and having the tool passage for receiving the
driven portion of the tool coaxial with an axis of rotation of the
spindle; and a tool retaining member connected to the tool
supporting element for releasably engaging the driven portion of
the tool to releasably retain the tool in the supporting element;
whereby in the maximum retracted position at which the tool is
retracted from the maximum insertion depth and the drive end is
still engaged in the first tool seat, the tool retaining member
still engages the driven portion.
62. The drive spindle of claim 61, wherein the axial length of the
first tool seat is 7 mm.
63. A drive spindle for rotatably supporting a tool in a dental
handpiece having a rotational torque generating drive, the tool
having a body divided into a driven portion with a driven end for
insertion into the handpiece and a working portion for extending
from the handpiece during use, the drive spindle comprising: a
driving element for receiving drive torque from the torque
generating drive; a tool supporting element connected with the
driving element and having a tool passage for receiving the driven
portion of the tool coaxial with an axis of rotation of the
spindle, the tool passage including a first tool seat for
supporting the driven end of the tool and a second tool seat for
supporting the driven portion at a location intermediate the driven
end and the working portion; the first tool seat having an axial
length for concentrically supporting the driven end when the tool
is retracted from a maximum insertion depth at which the driven
portion is fully inserted into the tool passage to a reduced
insertion depth at which the tool retaining member still engages
the driven portion; the driving element being a generally
cylindrical sleeve for receiving the driven portion of the tool and
the supporting element being a chuck coaxial with the sleeve; and a
tool engaging member for releasably engaging the driven portion to
releasably retain the tool in the tool passage between an
engagement depth at which depth the contact between the tool
engaging member and the driven portion is initiated and the maximum
insertion depth; the tool engaging member being positioned in the
spindle for engagement of the driven portion of the tool at a
location closer to the working portion than the driven end.
64. The drive spindle of claim 63, wherein the tool engaging member
is located on an inner surface of a wall portion of the chuck, the
wall portion being expandable upon insertion of the driven portion,
such that insertion of the driven portion into the bore forces the
wall portion to expand radially outward, the expanded wall portion
applying force radially inward against the driven portion such that
the tool engaging member frictionally engages the driven portion
for torque transfer and to prevent axial movement of the driven
portion relative to the chuck.
65. The drive spindle of claim 63, wherein the tool engaging member
comprises one or more protrusions extending radially inward from
the inner surface of the wall portion, the tool engaging member
either continuously or discontinuously extending annularly about
the axis of rotation.
66. The drive spindle of claim 64, wherein the wall portion further
comprises a pair of diametrically opposed axial retaining arms and
wherein a portion of the tool engaging member is located on an
inner surface of one or both of the retaining arms extending into
the bore.
67. The drive spindle of claim 66, wherein the retaining arms are
formed by two semi-circular wall portions of the chuck separated by
axial slits.
68. The drive spindle of claim 66, wherein the tool engaging member
is a tab or a discontinuous annularly extending ridge.
69. The drive spindle of claim 63, further comprising a ram axially
aligned with and adjacent to the chuck in the drive spindle, the
ram operatively engaging the chuck in a torque transfer
arrangement.
70. The drive spindle of claim 69, wherein the torque transfer
arrangement consists of a pair of diametrically opposed lugs for
engaging the axial slits in the adjacent wall portion of the
chuck.
71. The drive spindle of claim 63, wherein the ram is fitted into
the sleeve for drive torque transfer from the sleeve to the
ram.
72. The drive spindle of claim 63, wherein the chuck is in direct
contact with the drive for torque transfer to rotate the tool in
the handpiece.
73. The drive spindle of claim 63, further comprising a locking
socket of non-circular cross-section for engaging a complementary
non-circular cross-sectional portion of the driven portion to lock
the tool against rotation in the drive spindle, and a tool aligning
member positioned in the tool receiving bore near a tool insertion
end of the drive spindle for aiding in pre-alignment of the locking
portion with the locking socket, the tool aligning member being
complementary in shape and orientation with the locking socket.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. Application Ser.
No. 60/689,052, entitled Dental Burr And Drive Spindle, filed Jun.
10, 2005, and from U.S. application Ser. No. 11/262,959, entitled
Adjustable Tool Drive Arrangement, filed Nov. 1, 2005, which
applications are included herein by reference in their
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to handpieces for
rotating tools. More particularly, the present invention relates to
an improved drive arrangement for a rotatable tool, including a
drive spindle and the tool.
BACKGROUND OF THE INVENTION
[0003] Numerous handpieces for rotating tools exist. Turbine driven
handpieces are widely used in dental offices and medical labs
around the world. Most handpieces include a handle and drive head
for supporting the rotating tool. A connector, often a swivel
connector, connects the handpiece to various air, water, light and
power supply conduits, generally combined in a so-called umbilical
cord. The drive head houses a tool drive arrangement, generally
composed of a tool retaining mount or chuck, and a motor or
turbine, rotatably mounted in the head for driving the chuck. The
chuck releasably holds the tool, such as a dental bur, for rotation
about an axis of rotation.
[0004] In known handpieces, the tool is releasably held by the
chuck against axial movement in the drive arrangement. Screw lock
or pushbutton lock arrangements are provided for the manual locking
and releasing of the tool in and from the chuck. The known drive
arrangements are not designed to allow for length adjustment of the
tool, which means the tool, once fully inserted in the drive
arrangement will always protrude the same length from the drive
head. However, as a dental procedure progresses, a dentist may need
to use dental tools of different length. This creates the need for
repeated tool changes, which is time consuming and cost intensive,
since a collection of different length tools must be purchased.
[0005] In an attempt to find a time and cost efficient solution,
dentists often try to adjust the protruding length of the bur by
somewhat retracting the bur from the drive head until the desired
length is reached. However, this adjustment is made without
knowledge whether the bur will remain properly engaged within the
drive mechanism and safely secured within the drive head. This is a
dangerous practice, since prior art handpieces are not designed to
hold the bur in any position other than fully inserted into the
drive head. The tool when retracted may remain within the drive
head in the prior art handpieces due to the retaining force of the
friction arms normally included in the chuck. However, concentrical
support of the tool within the drive head and reliable torque
transmission from the drive to the tool are not ensured.
[0006] Conventional handpiece designs provide for concentrical
support of the tool in the fully inserted condition. Support is
provided at a rear, inserted end of the tool and at an intermediate
location of the tool corresponding to the area of the bottom
bearing in the drive head. However, upon even a minor retraction of
the tool from the fully inserted position, the tool is disengaged
from the concentrical support at the rear end of the tool. The tool
must then be maintained in axial alignment with the rotating drive
by way of the friction arms of the chuck. However, those friction
arms are somewhat flexible by design and generally do not provide
sufficient force to maintain the rear end of the tool
concentrically aligned in the drive when lateral forces are applied
to the working end of the tool during use. Therefore, operation of
a conventional handpiece at a tool insertion depth other than fully
inserted can result in loss of concentricity, vibration of the bur
during rotation, excessive wear, damage to the drive assembly,
permanent deformation of the tool securing mechanism and drive
spindle components, inefficient torque transfer, increased bur
slippage (both rotational and axial), and most dangerously,
accidental disengagement of the bur from the handpiece during
use.
[0007] Therefore, a need exists for a dental tool and handpiece
design allowing for tool depth adjustment without a loss of
concentricity.
[0008] Prior art chucks of dental handpieces are almost exclusively
designed to hold the dental bur by way of friction fit only.
Examples of such constructions are found in U.S. Pat. No.
3,869,796, U.S. Pat. No. 4,595,363, U.S. Pat. No. 5,275,558, and
U.S. Pat. No. 5,549,474. Only low torque transmission is possible
between the chuck and the bur in such constructions, higher torque
leading to slippage of the bur. At the high rotational speeds
achieved by modern dental handpieces, bur slippage, in both the
axial and rotational directions, can become a problem. Rapid
deceleration of the bur can also lead to rotational slippage, for
example, when the drive continues to rotate while the bur is locked
or snagged. Friction between the drive assembly and the dental bur
during rotation leads to significant wear of both elements over
time. This friction can also produce significant heat, as can
friction generated in push-button lock handpieces when the user
maintains pressure on the push-button during operation. Friction
heat can cause permanent damage to the drive spindle components,
especially the flexible friction arms of the chuck, which are
normally made of heat tempered material. The damage can lead to
rotational slippage and even axial slippage of the tool, possibly
resulting in an accidental release of the tool from the handpiece.
Accidental release of a dental bur during high speed rotation can
pose a threat to both the patient and the dentist. Continued wear
of the bur and drive assembly during operation necessitates routine
maintenance and repair of expensive handpiece components.
[0009] Thus, a drive spindle design is desired which not only
allows for adjustment of the exposed tool lengths but preferably
also prevents rotational slippage of the tool at all possible tool
retraction positions to avoid frictional wear and resulting heat
damage to the drive spindle.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to obviate or
mitigate at least one disadvantage of prior art handpiece
designs.
[0011] In a first aspect, the invention provides a tool drive
arrangement for a handpiece with a drive head, the tool drive
arrangement permitting length adjustment of the tool in the drive
head by concentrically supporting the tool in the drive head at any
position from a fully inserted position to a maximum retracted
position.
[0012] In a preferred embodiment, the tool drive arrangement
includes a tool and a rotatable tool supporting element for
concentrically supporting the tool from the fully inserted to the
maximum retracted position, the tool including a maximum retraction
indicator for indicating to a user when the tool has been retracted
to the maximum retraction position. This provides a significant
advantage over the prior art by allowing a user to adjust the
exposed length of a rotatable tool, preferably a dental bur,
without exceeding safe operating limits.
[0013] In a preferred embodiment of the tool, the tool includes a
tool body having an axis of rotation, the tool body being divided
into a driven portion with a driven end for insertion into the tool
supporting element, and a working portion for projection from the
drive head during use. The tool further includes a maximum
retraction indicator on the driven portion for indicating to a user
when the tool is retracted from the fully inserted position to the
maximum retraction position.
[0014] In another preferred embodiment, the tool supporting element
is a drive spindle for concentrically supporting the tool at
different insertion depths from a maximum insertion depth at the
fully inserted position to a minimum insertion depth at the maximum
retraction position. The drive spindle includes a drive torque
receiving portion, a tool supporting portion with a tool passage
for receiving the driven portion of the tool and a tool retaining
member for releasably retaining the driven portion in the tool
passage. The tool supporting portion includes a first tool seat for
supporting the drive end of the tool and a second tool seat for
supporting the driven portion at a location intermediate the driven
end and the working portion of the tool. The first seat has a
sufficient axial length for concentrically supporting the driven
end when the tool is retracted from the fully inserted position to
a retracted position wherein the retaining member still engages the
driven portion.
[0015] In one aspect, the maximum retraction indicator is a visible
indicia located on the driven portion, intermediate the driven end
and the working portion, to be hidden from view when the tool is
inserted at a depth between the maximum and minimum insertion
depths and visible to a user when the tool is retracted from the
drive head to the maximum retraction position or further.
Preferably, the maximum retraction indicator is selected from the
group of at least one dot, line, colored line, etched line, a line
having a surface roughness different from the remainder of the
driven portion, a change in diameter of the tool and a groove. The
line or groove can be continuous or broken, such as a line of dots.
The line or groove can extend in circumferential or longitudinal
direction of the tool or at any angular orientation therebetween.
The maximum retraction depth can be indicated by an end or an edge
of the line or groove. The maximum retraction depth can also be
indicated by a change in the overall appearance of the line or
groove, such as a change in color, a change in size, a change in
any other characteristic, or any combination thereof.
[0016] In another aspect, the maximum retraction indicator is a
mechanical indicia located on the driven portion for engagement by
a portion of the tool supporting element when the maximum
retraction depth is reached. Preferably, this mechanical engagement
provides a tactile indication, possibly even an auditory indication
(click), to the user that the maximum retraction depth is reached.
In a preferred embodiment, the mechanical indicia is a stop on the
driven portion of the tool for mechanical interaction with the tool
retaining member of the tool supporting element when the tool is
retracted to the maximum retraction depth. Preferably, the tool
supporting element includes a tool retaining member for
frictionally retaining the tool and the tool further includes a
contact surface on the driven portion for engagement by the tool
retaining member at insertion depths from the maximum insertion
depth to at least the minimum insertion depth. The stop is
preferably a stop shoulder on the contact surface of the tool for
axial engagement by the tool engaging member when the tool is
retracted from the maximum insertion depth to the maximum
retraction depth.
[0017] In one variant, the contact surface is a detent on the
driven portion and the stop is an axial end shoulder of the detent.
In a particularly preferred embodiment, frictional engagement of an
elongated detent by the tool retaining member allows the tool to be
positioned in the handpiece at any insertion depth between the
minimum insertion depth (or maximum extraction depth) and the
maximum insertion depth. In another variant, the tool comprises two
or more detents on the driven portion, each having a stop shoulder
for axial engagement with the tool engaging member for defining one
or more intermediate insertion depths between the minimum tool
insertion depth and the maximum retraction depth. In a particularly
preferred embodiment, the detent is a groove extending
circumferentially about the driven portion of the tool.
[0018] Those skilled in the art will appreciate that the tool
insertion depth indicator and tool retaining member can be achieved
by other means than those described in the preferred embodiments of
the invention without deviating from the essence of the invention.
It will also be apparent that more than one tool retaining member
can be provided in the tool supporting element while preserving the
core function.
[0019] It is a significant advantage, of an adjustable length tool
drive arrangement in accordance with the invention allowing axial
adjustment of tool insertion depth in a dental handpiece, that the
number of times a dentist must exchange tools for selection of
different tool lengths during the course of a dental procedure is
reduced. This reduces the time required to perform the procedure
and can reduce operating cost, since fewer tools of specific length
need to be purchased and maintained. It is another significant
advantage that, by providing the preferred maximum retraction
indicator, excessive wear and damage due to insufficient insertion
of the tool in the handpiece are avoided.
[0020] In an alternate embodiment, the minimum tool insertion depth
indicator is a combination of a mechanical and a visual
indicator.
[0021] In a preferred embodiment of the tool supporting element,
the drive spindle has a chuck including the tool supporting portion
and the tool retaining member. The tool passage is an axial bore in
the chuck for receiving the driven portion of the tool up to the
maximum insertion depth. The tool retaining member is a resilient
tool engaging member for releasably frictionally engaging a contact
surface on the driven portion of the tool from an engagement depth,
at which depth contact between the tool engaging member and the
driven portion is initiated during tool insertion, to the maximum
insertion depth. In a preferred embodiment, the tool engaging
member is shaped and constructed to axially engage a maximum
retraction depth indicator on the tool in the form of a stop
shoulder on the contact surface, when the tool is retracted from
the maximum insertion depth to a maximum retraction depth located
between the maximum insertion depth and the engagement depth. The
tool engaging member is shaped and constructed to frictionally
engage the driven portion to prevent axial movement of the tool in
the spindle during operation of the handpiece.
[0022] In a preferred embodiment, the chuck is a generally
cylindrical member having the tool receiving axial bore. A portion
of the wall surrounding the bore is resiliently deformable and
forms the resilient tool engaging member to allow insertion of the
driven portion of the tool into the bore. When the tool is
inserted, the chuck wall portion forming the tool engaging member
radially inwardly engages the driven portion to frictionally retain
the tool in the bore. Axial engagement of the tool engaging member
with a first stop shoulder on the contact surface of the tool
provides a maximum tool retraction indication.
[0023] In a particularly preferred embodiment, the resilient wall
portion of the chuck forms of a pair of diametrically opposed
axially extending retaining arms, at least one of which has a
radially inwardly projecting protrusion extending therefrom for
frictionally engaging the contact surface of the tool and for
axially engaging a mechanical retraction depth indicator on the
tool, such as the maximum retraction depth indicator. In a
preferred embodiment, the drive spindle of the present invention
further comprises a ram for selectively forcing apart the retaining
arms to allow insertion and/or removal of the tool. The ram is
axially aligned with and adjacent the chuck in the drive spindle,
and operatively engages the chuck in a torque transfer arrangement.
In a particularly preferred variant, a hollow cylindrical sleeve is
provided for supporting the chuck and the ram in this axially
aligned configuration. Various tool drive arrangements are
contemplated in accordance with the present invention, which can
allow for torque transfer from the drive to the sleeve, from the
drive to the chuck, from the drive to the ram, or from the drive
directly to the rotatable tool.
[0024] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Embodiments of the present invention will now be described,
by way of example only, with reference to the attached Figures,
wherein:
[0026] FIG. 1 is a cross-sectional view of a known dental handpiece
suitable for use with a tool drive arrangement in accordance with
the present invention;
[0027] FIG. 2 illustrates a perspective view of a rotatable tool
and drive spindle components of a tool drive arrangement in
accordance with a preferred embodiment of the present
invention;
[0028] FIGS. 3A to 3F show perspective views of dental tools
including different types of maximum retraction indicators in
accordance with various preferred embodiments of the tool aspect of
the invention;
[0029] FIG. 3G shows an alternative preferred embodiment of the
dental tool with two mechanical depth indicators, including the
maximum retraction indicator, located on the locking portion of the
tool, as well as a visual indicator of maximum retraction;
[0030] FIG. 4A is an axial end view of the dental bur shown in FIG.
3D illustrating a torque lock;
[0031] FIG. 4B is an axial end view from the driven end of the
dental bur of FIG. 3F or 3G illustrating an alternative torque lock
to that exemplified in FIG. 4A;
[0032] FIG. 4C shows a cross-sectional end view through the locking
portion of the dental bur of FIG. 3G taken through line A-A;
[0033] FIG. 5 illustrates a perspective view of a preferred
embodiment of a dental bur type tool of the invention having a
mechanical maximum retraction indicator in the form of a single,
axially elongated detent for continuous depth adjustment;
[0034] FIGS. 6A and 6B illustrate perspective front and rear end
views of a preferred embodiment of a chuck of the tool supporting
element aspect of the present invention;
[0035] FIGS. 6C and 6D illustrate alternative preferred embodiments
of the chuck of the tool supporting element aspect of the present
invention, illustrating a double-tab variant (6C) and a single-tab
(or asymmetrical tab) variant (6D);
[0036] FIG. 7 illustrates an end view from the tool receiving end
of the drive spindle of FIG. 2, but shown in assembled
condition;
[0037] FIG. 8 illustrates an end view from the driven end of the
drive spindle of FIG. 7;
[0038] FIGS. 9A and 9B illustrate axial cross-sections of the tool
drive arrangement of FIG. 2;
[0039] FIG. 10 illustrates an axial cross-section through the tool
and tool drive arrangement combination of FIG. 2, in an assembled
condition and with the dental tool of FIG. 3D inserted into the
spindle to the maximum insertion depth;
[0040] FIG. 11 illustrates the assembled drive arrangement and tool
combination shown in FIG. 10, but with the tool retracted to the
maximum retraction length;
[0041] FIG. 12 illustrates an alternative preferred embodiment of
the tool drive arrangement of the invention having a drive spindle
and the asymmetrical chuck of FIG. 6D, in combination with the tool
of FIG. 3G;
[0042] FIGS. 13A and 13B illustrate axial cross-sections through
the drive arrangement of FIG. 12 in an assembled condition with
FIG. 13B rotated 90.degree. about the axis in relation to FIG.
13A;
[0043] FIG. 14 illustrates an axial cross-section through the drive
arrangement as shown in FIG. 13A, with a dental tool as shown in
FIG. 3G inserted into the spindle; and
[0044] FIG. 15 shows a cross-section through the locking socket of
the sleeve of FIG. 13B, taken along line C-C, and illustrates a
locking portion of the tool of FIG. 3G positioned therein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] Generally, the present invention provides a tool drive
arrangement for a handpiece with a drive head, the tool drive
arrangement permitting length adjustment of a tool in the drive
head by concentrically supporting the tool in the drive head at any
position from a fully inserted position to a maximum retracted
position.
[0046] In one embodiment, the invention provides a tool drive
assembly including the tool drive arrangement, a rotatable tool and
a rotatable tool supporting element for concentrically supporting
the tool from the fully inserted position to the maximum retracted
position. The tool preferably includes a maximum retraction
indicator for indicating to a user when the tool has been retracted
to the maximum retraction position. This provides a significant
advantage over the prior art by allowing a user to adjust the
exposed length of a rotatable tool, preferably a dental bur,
without exceeding safe operating limits.
[0047] More particularly, the rotatable tool drive assembly in
accordance with the invention includes a rotatable tool and a tool
supporting element for releasably supporting the tool. The tool
supporting element is insertable into a drive head for coaxial
rotation in the drive head. The tool has a tool body having an axis
of rotation and is divided into a driven portion, with a driven end
for insertion into the tool supporting element, and a working
portion for projecting from the drive head during use. The tool
supporting element has a tool passage for coaxially receiving the
driven portion of the tool and supporting it at different insertion
depths, the tool passage including a first tool seat for
concentrically supporting the driven end of the tool and a second
tool seat for concentrically supporting the driven portion at a
location intermediate the driven end and the working portion. In a
preferred embodiment, the first tool seat is axially elongated for
concentrically supporting the driven end at any position from a
maximum insertion position, wherein the tool is fully inserted into
the tool passage, to a maximum retraction position, wherein the
tool is retracted from the maximum insertion position.
[0048] The invention will now be described in more detail with
reference to specific preferred embodiments of the invention
directed to an improved tool drive arrangement and tool, wherein
the tool is a dental tool such as a bur, and the tool supporting
element is a drive spindle, such as a drive spindle for use in a
high speed turbine-driven dental handpiece. Although specific
reference is made in the following to a dental bur and a drive
spindle for a high speed dental handpiece, it will become apparent
to those skilled in the art that all structural and functional
features of the invention are equally applicable to rotatable
dental and medical tools in general and to medical and dental
handpieces and other handpieces for supporting high speed rotating
tools.
[0049] A high speed dental handpiece 100, as shown in FIG. 1
generally includes a handle 102, a tool supporting drive head 101,
and a swivel connector (not illustrated) for connecting the
handpiece to various air, water, light and power supply conduits,
generally combined in a so called umbilical cord (not shown). The
drive head 101 includes a torque producing drive 105, typically a
motor or turbine rotatably mounted in the drive head, and having a
spindle socket 109 for housing a tool supporting element 103, here
a drive spindle 10. The tool supporting element 103 typically
includes a tool receiving and retaining portion, here a chuck 20,
constructed to releasably retain a tool 106, such as a dental bur,
for rotation about an axis of rotation 108. The tool supporting
element 103 may be retained in the drive head 101 by any means
known in the art, for example, by press-fitting the tool supporting
element 103 in the spindle socket 109 of the drive head.
[0050] Referring now to FIGS. 1 to 3G, a dental tool 106, such as
the dental bur 50, typically has an elongated body 52 divided into
a generally cylindrical driven portion 54 for insertion into the
drive head 101 of a dental handpiece 100 for receiving drive torque
from the drive 105 of the handpiece, and a working portion 56 for
projecting from the drive head 101 of the handpiece in an operating
condition. The working portion has a working end 58 for engagement
with a working surface, such as a tooth surface (not illustrated),
during a dental procedure. The user, typically a dentist, must
purchase a collection of burs varying in shaft length as well as in
the structure of the working end 58 of the working portion 56. The
dental bur 50 is generally inserted into the spindle 10 in the
drive head 101 and is removably supported therein by the chuck 20
for rotation with the spindle 10 about the axis of rotation
108.
[0051] As illustrated in FIG. 2, a preferred embodiment of the tool
drive arrangement of the present invention provides an improved
drive spindle 10, to be described in more detail below, for use
with an improved dental bur 50 in accordance with the tool aspect
of the invention.
[0052] Different preferred embodiments of the tool aspect of the
present invention are now described by reference to the various
preferred dental bur embodiments shown in FIGS. 3A to 3G. The
dental bur 50 illustrated in FIGS. 3A to 3G includes a body 52
having an axis of rotation 52a, a working portion 56 for projecting
from the drive head 101 (see FIG. 1) of a dental handpiece 100
during use, and a driven portion 54 for insertion into the drive
head for directly or indirectly receiving drive torque. All
illustrated burs include a maximum retraction indicator 107, which
can be either a visible indicator 57 as shown in the burs of FIGS.
3A to 3C, a mechanical indicator 59 as shown in the bur of FIG. 3D
or 3F, or a combination of visible and mechanical indicator as
shown in FIGS. 3E and 3G.
[0053] A visible indicator 57, as shown in the burs of FIGS. 3A to
3C, 3E and 3G is preferably provided on or in the surface of the
driven portion 54 of the bur 50 such that the indicator is not
visible at the maximum tool insertion depth. When the driven
portion 54 is retracted from the maximum insertion depth toward the
maximum retraction depth, for depth adjustment, the visual
indicator 57 becomes apparent to the user, preferably only when the
maximum tool retraction position (or minimum tool insertion depth)
is reached. A few examples of visual indicia include, but are not
limited to, a dot, a line, a colored line, an etched line, a laser
mark, a line having a surface roughness different from the
remainder of the driven portion, a detent and a groove. The visual
indicator 57 can extend completely or partially circumferentially
about the driven portion 54 as shown in FIGS. 3B and 3G,
respectively, axially along the driven portion 54 as shown in FIG.
3A, or at an angular orientation to the axis of rotation 108 (not
shown). If the visible indicator 57 extends axially as shown in
FIG. 3A, the maximum retraction position can be indicated by the
start or end of the indicator, by an edge of the indicator, or by a
change in the overall appearance of the indicator, such as a change
in color, a change in size, a change in any other characteristic,
or any combination thereof. This is shown in FIG. 3A which
illustrates a bur 50 with a visual indicator 57 having sections 57a
to 57c of different characteristics (preferably colour), whereby
the maximum extraction depth is indicated by the transition from
section 57b to section 57c becoming visible to the user.
[0054] As exemplified in the embodiment of FIG. 3D, the bur 50 has
a contact surface 60 on the driven portion 54 for frictional
engagement by a tool engaging member 15 of the spindle 10, to be
discussed in more detail below in relation to FIG. 2. The tool
engaging member 15 engages the contact surface 60 at insertion
depths of the tool from an engagement depth, at which contact
between the tool engaging member 15 and the driven portion 54 is
initiated, to a maximum insertion depth, at which the bur 50 is
fully inserted into the handpiece 100. In this embodiment, the
mechanical type maximum retraction indicator 59 includes a first
stop shoulder 68 on the contact surface 60 for axial engagement
with the tool engaging member 15 when the bur 50 is retracted from
the maximum insertion depth (D.sub.max) to a maximum retraction
depth (D.sub.min) between the engagement depth and the maximum
insertion depth (see FIGS. 10 and 11).
[0055] The bur of FIG. 3E includes both the visible indicator 57
shown in FIG. 3B and the mechanical indicator 59 shown in FIG. 3D.
The bur shown in FIG. 3G includes a visible indicator 57 in the
form of a laser mark as well as the mechanical indicator 59 as
shown in FIGS. 3D to 3F.
[0056] In a preferred embodiment as shown in FIG. 2, the mechanical
type maximum retraction indicator 59 is a detent 51 located on the
driven portion 54, the detent having a first axial stop shoulder 68
for axial engagement by the tool engaging member 15 of the drive
spindle 10 for indicating the minimum insertion depth (D.sub.min)
(or maximum retraction depth) of the bur 50 in the drive spindle
10. D.sub.min is essentially the depth at which the working portion
56 is maximally extended from the handpiece while the driven
portion 54 is still concentrically supported in the drive spindle
10 and properly engaged with the drive mechanism in the handpiece
for reliable torque transfer. D.sub.min can be easily determined
for various handpiece and spindle designs without undue
experimentation. A conservative D.sub.min can be also be selected
which is greater than the depth at which the working portion 56 is
maximally extended from the handpiece. The difference between
D.sub.min and D.sub.max provides a length of axial play along which
the bur 50 can be safely adjusted in the drive spindle 10.
[0057] As illustrated in the preferred embodiment shown in FIG. 2,
a second retraction depth indicator 107a can be provided on the
driven portion 54 for defining a corresponding second or
intermediate insertion depth of the driven portion 54 in the drive
spindle 10 between D.sub.min and D.sub.max, and including
D.sub.max. The preferred embodiment illustrated in FIG. 3D shows
two annular circumferential detents 51 on the driven portion 54,
those being the maximum retraction depth indicator 59 and an
intermediate insertion depth indicator 59a, having first and second
stop shoulders 68 and 68a respectively for axial engagement with
the tool engaging member 15 upon retraction (see FIG. 2) of the
driven portion 54 from the maximum insertion depth toward the
intermediate insertion depth, D.sub.min, or the engagement depth.
Axial engagement of the first axial stop shoulder 68 by the tool
engaging member 15 indicates that D.sub.min is reached. In the
variant shown in FIG. 3D, axial engagement of the second stop
shoulder 68a by the tool engaging member 15 occurs when the tool is
inserted to essentially D.sub.max (see FIG. 10). The second stop
shoulder 68a thus serves to retain the driven portion 54 at
D.sub.max, during operation of the handpiece, while the first stop
shoulder 68 serves to retain the driven portion 54 at D.sub.min
during operation with a maximally extended bur 50 (see FIG.
11).
[0058] The bur exemplified in FIG. 3G also includes an intermediate
mechanical retraction depth indicator 59a on the driven portion 54.
Intermediate retraction depth indicators (mechanical and/or visual)
can be provided on the bur to indicate to a user when the maximum
insertion depth (D.sub.max) or any desired intermediate insertion
depth has been reached. With the mechanical indicator, the user
preferably perceives a tactile indication (i.e. a snap) and/or
auditory indication (i.e. a click) upon engagement of a mechanical
indicator by the tool engaging member 15.
[0059] Alternative embodiments of the mechanical retraction depth
indicator of the present invention include, but are in no way
limited to: (a) a single axially elongated detent 51 on the driven
portion 54 as illustrated in FIG. 5, for continuous depth
adjustment wherein frictional engagement of the contact surface 60
of the detent 51 by the tool engaging member 15 allows the tool to
be securely positioned in the handpiece at any insertion depth
between D.sub.min and D.sub.max during operation of the handpiece,
D.sub.min being indicated by axial engagement of the first stop
shoulder 68 by the tool engaging member 15; (b) a plurality of
insertion depth indicators 59 as shown in FIGS. 3D and 3G, each
having a stop shoulder 68 located on the driven portion 54 for
defining a plurality of corresponding intermediate insertion depths
between D.sub.min and D.sub.max, D.sub.min being indicated by the
first axial stop shoulder 68 of the maximum retraction depth
indicator 59; (c) a contoured annular maximum retraction depth
indicator that gradually tapers radially outward axially from the
first stop shoulder in the direction of the working portion 56 (not
illustrated), wherein frictional engagement of the contact surface
of the tapered annular detent by the tool engaging member 15 allows
the driven portion 54 to be positioned in the handpiece at any
insertion depth between D.sub.min and D.sub.max, D.sub.min being
indicated by the first axial stop shoulder 68.
[0060] Although for ease of manufacture the mechanical indicator 59
described above is preferably in the form of a recessed detent 51
on the contact surface 60 of the driven portion 54, it will be
readily understood that the indicator, and especially the stop
shoulder 68, could be in the form of an elevation protruding from
the surface of the driven portion 54. As will become apparent to
persons of skill in the art, other indicator variants can serve as
the mechanical indicator to indicate when a desired insertion depth
has been reached and as such are considered to be within the scope
of the present invention.
[0061] In accordance with a preferred embodiment, a detent is any
type of recess located on the body 52 of the bur 50, but is
preferably an annular, circumferentially extending groove on the
driven portion 54. An axially elongated detent or a plurality of
axially spaced apart annular detents on the driven portion 54 allow
for safe and controlled axial adjustment of the bur 50 in the drive
spindle 10 at a range of depths between D.sub.max and a
predetermined D.sub.min, thereby providing for "depth indexing".
The provision of safe tool depth adjustment and controlled depth
indexing in a dental handpiece satisfies a long felt need in the
art.
[0062] Operation of the handpiece at tool insertion depths between
D.sub.min and the engagement depth is also possible due to
frictional engagement of the driven portion 56 by the tool engaging
member 15 but is not preferred due to the disadvantages associated
with bur overextension.
[0063] The terms "maximum retraction indicator", "maximum
retraction depth indicator", "minimum insertion depth indicator",
"minimum tool insertion depth indicator", and similar terms, are
used interchangeably herein. Similarly, the terms "maximum
retraction position", "maximum retraction length", "maximum
retraction depth", "minimum insertion depth", and similar terms,
are used interchangeably herein. In this context, the terms
"retracted" or "retraction" indicate that the tool is retracted
from the maximum insertion depth, at which depth the tool is fully
inserted into the drive spindle, toward the working end of the
drive spindle. In contrast, the terms "inserted" or "insertion"
refer to insertion of the tool into the working end of the drive
spindle toward the driven end of the spindle.
[0064] In a preferred embodiment of the present invention,
illustrated in FIGS. 2 and 7 to 11, the tool supporting element, in
this embodiment the spindle 10, is insertable into the spindle
socket 109 of the drive head 101 for coaxial rotation in the drive
head. The tool 106, here the bur 50, has a tool body 52 with axis
of rotation 108, a driven portion 54 with driven end 55 for
insertion into the spindle 10, and a working portion 56 for
projecting from the drive head during use. As shown in FIGS. 10 and
11, the spindle 10 has a tool passage 12 for coaxially receiving
the driven portion 54 of the tool at different insertion depths,
the tool passage 12 including a first tool seat 14 for
concentrically supporting the driven end 55 of the bur 50 and a
second tool seat 16 for concentrically supporting the driven
portion 54 of the bur 50 at a location intermediate the driven end
55 and the working portion 56. The first tool seat 14 is axially
elongated for concentrically supporting the driven end 55 at any
position from a maximum insertion position (D.sub.max), wherein the
bur 50 is fully inserted into the tool passage 12 (FIG. 10), to a
maximum retraction position (D.sub.min), wherein the bur 50 is
retracted from the maximum insertion position (FIG. 11). In a
preferred embodiment of the first tool seat 14, the axial length
(depth) of the first tool seat is at least equal to 10% of the
axial length of the driven portion 54 of the bur 50 used in
combination with the spindle 10. To obtain a sufficiently large
retraction length, the axial length (depth) of the first tool seat
14 is more preferably at least 15% of the axial length of the
driven portion 54, most preferably at least 20%. Practical
retraction ranges are achievable when the axial length (depth) of
the first tool seat 14 is 15 to 60% of the axial length of the
driven portion 54, more preferably 20 to 75%, although other length
ratios are also within the confines of the present invention. The
axial length of the first tool seat 14 can also be selected
independent of the length of the driven portion 54 of the bur 50
used in combination therewith, preferred seat lengths being at
least 1.5 mm, more preferably at least about 2 mm, more preferably
about 2-7 mm and most preferably about 5 mm.
[0065] The spindle 10 of the preferred embodiment of the tool
supporting element shown in FIG. 2 (as shown in FIGS. 9A, 9B, 10,
11) includes a torque receiving element in the form of a generally
cylindrical casing sleeve 30 which fits into the spindle socket 109
of the drive head 101 for receiving rotational torque from the
drive 105. The casing sleeve 30 houses a tool supporting element,
in the form of a chuck 20, for releasably supporting the bur 50,
and a ram 40 for selectively releasing the bur 50 from the chuck
20. The chuck 20 includes the tool passage 12 in the form of a tool
receiving axial bore 22 for receiving the driven portion 54 of the
bur 50 coaxial with the axis of rotation 108. The axial bore
preferably extends from a driven chuck end 21 of the chuck 20 to
the tool receiving end 23. The chuck 20 further includes a tool
retaining member 104 in the form of a resilient tool retaining arm
24. The tool passage 12 includes the first tool seat 14 for
supporting the driven end 55 of the bur 50 and the second tool seat
16 for supporting the driven portion 54 at a location intermediate
the driven end 55 and the working portion 56. In the spindle 10
embodiment exemplified in FIGS. 9A and 9B, the first tool seat 14
is located in the chuck 20 and the second tool seat 16 is located
in the ram 40. In this embodiment, the first tool seat 14 has a
sufficient extent in axial direction (sufficient depth) to
concentrically support the driven end 55 of the tool even when the
tool is retracted from the maximum insertion depth D.sub.max, at
which depth the driven portion 54 is fully inserted into the tool
passage 12, to a retracted position at which position the tool
retaining member 15 still engages the driven portion 54.
[0066] The tool retaining arm 24 is formed by a resilient portion
of the chuck wall 13 surrounding the axial bore 22. The retaining
arm 24 is preferably radially resiliently deflectable for insertion
of the driven portion 56 into the bore 22. The retaining arm 24
preferably has a tool engaging tab 25 for contact with the contact
surface 60 of the bur 50. The retaining arm is made of a
sufficiently strong material (preferably stainless steel) to bias
the tool engaging tab 25 against the contact surface 60 with
sufficient force, once the driven portion 54 is inserted into the
axial bore 22, to frictionally engage the bur 50 for torque
transfer and to prevent axial movement of the bur 50 in the drive
spindle 10 during operation of the handpiece 100. The selection of
appropriate materials for the chuck 20 and the retaining arm 24 is
not part of the present invention and is well within the abilities
of the art skilled person. It will also be readily apparent to the
art skilled person that the chuck 20 may be provided with multiple
retaining arms 24, such as the pair of diametrically opposite
retaining arms 24 shown in the embodiments of FIGS. 6A to 6D. In
one embodiment, the retaining arm 24 extends towards the tool
receiving end 23 of the chuck 20 in the spindle (see FIGS. 10 and
11) and the tool engaging member 15 is located near the tool
receiving end 23 for frictional engagement with the driven portion
56. This orientation allows for a larger retraction range than with
a retaining arm 24 extending toward the driven chuck end 21 of the
chuck 20 in the spindle (FIGS. 12 and 14) since the bur 50 must
still be held by the retaining arm 24 at maximum retraction.
[0067] In the embodiment of the tool drive arrangement of the
invention shown in FIGS. 10 and 11, the chuck 20 is constructed for
interaction with the mechanical maximum retraction indicator 59 on
the bur 50 to indicate D.sub.min. To that end, the tool engaging
tab 25 protrudes radially inwardly from the retaining arm 24 and is
sized and shaped to not only fit into the mechanical maximum
extraction indicator 59, in this embodiment an indicator groove 70,
but to also to generate a tactile sensation for the user to
indicate that D.sub.min has been reached. In this manner, the user
will preferably insert the bur 50 into the chuck 20 until D.sub.max
is reached, which is apparent from the fact that no further
insertion of the bur is possible, and then retract the bur 50 to
the desired position. Over-retraction of the bur 50 from the chuck
20 is avoided by the tactile sensation of the tool engaging tab 25
snapping into the indicator groove 70 which is felt, and in some
cases heard, by the user when D.sub.min is reached.
[0068] Engagement of the tool engaging tab 25 of the retaining arm
24 with the indicator groove 70 also provides an additional safety
feature not available in conventional handpiece designs. ISO
recognizes excessive heat as one of the major contributing factors
to chuck fatigue and failure in conventional handpieces. To avoid
the generation of excessive heat by the user maintaining pressure
on the bur release push button of a turbine handpiece, one of the
ISO standards stipulates the minimum set back force of the push
button resetting spring. The intention of that standard is to avoid
friction between the push button mechanism and the spindle of the
handpiece during rotation of the turbine. Excessive heat not only
reduces lubrication, but more importantly can lead to relaxation of
the spring force of the bur retaining arms of the chuck. Those arms
are generally made of tempered steel and excessive heat leads to
creep of the tempered material, thereby relaxing their resetting
force. Once relaxation has occurred, the bur may no longer be
reliably retained in the chuck. This problem is overcome with the
embodiment of the tool drive arrangement of the invention shown in
FIGS. 10 and 11, for example, wherein the tool engaging tab 25 on
the retaining arm 24 engages the indicator groove 70. This
mechanical engagement can be achieved even after heat relaxation of
the retaining arm 24, so that the bur 50 is more reliably retained
in the chuck 20.
[0069] In one variant, as illustrated in FIGS. 10 and 11, the bur
50 includes the indicator groove 70 as well as a maximum insertion
groove 72 into which the tool engaging tab 25 snaps when the bur 50
is fully inserted into the chuck 20. This provides a tactile
sensation to the user at both maximum insertion (D.sub.max) and
maximum retraction (D.sub.min) of the bur 50. In another variant
(not illustrated), the bur 50, in addition to the indicator groove
70 and the maximum insertion groove 72, includes one or more
intermediate insertion grooves located therebetween (not shown)
which each cooperate with the tool engaging tab 25 to provide a
tactile sensation to the user. These additional grooves can be
spaced along the driven portion 54 at selected intervals to provide
a `depth indexing` or `retraction length indexing` function. In yet
a further variant (not illustrated), the multiple annular indexing
grooves can be replaced with a helical indexing groove extending
along the driven portion 56 of the bur 50, allowing for depth
indexing of the bur by rotating the bur 50 relative to the chuck 20
while the tool engaging tab 25 is engaged in the helical groove.
Multiple helical grooves can also be provided.
[0070] In the preferred embodiment exemplified in FIGS. 9A and 9B,
the chuck 20 includes a pair of diametrically opposed retaining
arms 24 formed by two semi-circular wall portions of the chuck 20
which are separated by axial slits 26. The tool engaging tab 25
(see FIGS. 6A and 6B) is formed by one or more protrusions
extending radially inward from an inner surface of the retaining
arms 24 about the central axis 29 for frictionally engaging the
contact surface 60 of the driven portion 54 to prevent axial
movement of the bur 50 during operation of the handpiece 100, and
for axial engagement with the first axial end shoulder 68 of the
maximum retraction indicator 59 (see FIG. 2) for indicating when
D.sub.min is reached.
[0071] In another variant (FIG. 6C), the tool engaging tab 25 is
formed by a pair of diametrically opposed annular ridges protruding
from the inner surfaces of two opposed semi-circular retaining arms
24. The retaining arms and tool engaging tabs can be constructed
and achieved by any means known to those skilled in the art. For
instance, the retaining arms 24 may be straight with generally
parallel axially extending sides, as shown in FIGS. 6A and 6B, or
they may be tapered as shown in FIGS. 6C and 6D. It will further be
appreciated by those of skill in the art that there may be more
than two retaining arms, preferably arranged in a symmetrical
fashion for vibration-free rotation at high speeds.
[0072] The tool engaging tabs 25 may be of any suitable shape and
design, for example, they may be square or rectangular in profile
(FIGS. 10, 11), angled at one axial end in profile (FIGS. 6A to
6C), angled at both axial ends in profile (FIG. 6D), or they may
have a different shape altogether, such as rounded, so long as the
retaining function is reliably achieved. To aid in guiding the bur
50 into the chuck 20, the surface of the tabs 25 at the tool
receiving end of the retaining arms 24 can be angled toward the
central axis 12 of the tool receiving bore 22, similar to the tab
shown in FIG. 6D. In the tool drive arrangement illustrated in FIG.
12, which encompasses the chuck of FIG. 6D, the angled tab 25
actually aids in aligning the lugs 44 of the ram 40 within the
axial slits 26 of the chuck 20 in the assembled condition of the
spindle 10.
[0073] The depth to which a tool engaging tab 25 extends into a
mechanical retraction indicator 59 or 59a, preferably a detent 51
or groove 70 on the bur 50, can be varied, for example, depending
on design and materials. The tab height may be less than, equal to,
or more than the depth of the groove. When the tab 25 height is
equal to or less than the depth of the detent 51, or groove 70,
this prevents excessive deformation of the retaining arms when the
bur is inserted therebetween with the tab or tabs engaged in a
mechanical indicator 59 or 59a. Such an arrangement also ensures
maximal frictional engagement of the bur by the retaining arms for
reduced rotational and axial slippage.
[0074] In the embodiment of the tool drive arrangement shown in
FIG. 2, as seen in FIGS. 9A and 9B, the drive spindle 10 further
includes a ram 40 for radially forcing apart the retaining arms 24
during insertion and retraction or removal of the bur 50. In this
embodiment, the ram 40 is mounted in the casing sleeve 30 at the
tool insertion end 13 of the drive spindle 10 and is axially
aligned with and adjacent to the chuck 20. The ram 40 has a central
tool opening 42 for passage of the bur 50 and a pair of
diametrically opposed lugs 44 extending axially from the ram 40
toward the chuck 20 in the assembled condition of the spindle 10.
The lugs 44 are shaped to engage the axial slits 26 of the chuck 20
in the assembled condition. The lugs 44 are preferably
longitudinally tapered to force apart the retaining arms 24 when
the ram 40 and chuck 20 are forced toward one another. The ram 40
is preferably fastened to the casing sleeve 30 and the chuck 20 is
preferably movable in the casing sleeve 30 to allow for movement of
the chuck 20 relative to the ram 40 for use of the spindle 10 in
pushbutton release handpieces. Activating the pushbutton of such a
handpiece (not illustrated) will move the chuck 20 in the casing
sleeve 30 toward the ram 40 whereby the retaining arms 24 are
radially forced apart by the lugs 44, as will be readily apparent
to the person skilled in the art. The ram 40 is permanently or
releasably fastened to the casing sleeve 30, for example, by a
threaded connection or a press-fit. Other possible fastening
methods include welding or gluing and the like. However, the
fastening method used must ensure that the ram 40 will not move
relative to the casing sleeve 30 when the ram and chuck are forced
against one another for the opening of the retaining arms 24.
[0075] In one variant of the spindle 10, the casing sleeve 30
represents the torque receiving element of the spindle. The sleeve
30 fits sufficiently closely into the spindle socket 109 of the
drive head 101 (see FIG. 1) to ensure reliable torque transfer from
the drive 105 to the spindle 10. Rotational torque is then
transferred from the spindle 10 to the bur 50 through engagement of
the lugs 44 of the ram 40 in the axial slits 26 of the chuck 20 and
frictional engagement of the retaining arms 24 with the contact
surface 60 on the bur 50. In a preferred variant of the spindle 10,
as shown in FIGS. 6A and 6B, torque is transferred directly from
the drive 105 to the chuck 20 by way of a torque key 28 on the
driven chuck end 21 of the chuck 20, which is shaped for fitting
engagement with a torque socket (not illustrated) at a bottom of
the spindle socket 109. The torque key 28 is formed by providing
the driven chuck end 21 with any non-circular outer cross-section.
The torque key 28 and the torque socket preferably have
complementary shapes, but non-complementary shapes providing an
interference fit can also be used as long as rotation of the torque
key 28 relative to the torque socket is reliably prevented. In a
preferred embodiment, the non-circular torque key 28 is shaped from
a generally cylindrical end portion of the chuck 20 which is
provided with two diametrically opposed flattened surface portions
(see FIGS. 6B and 8).
[0076] In a preferred embodiment of the drive arrangement, the
drive arrangement further includes a structure for locking the bur
50 against rotation in the tool passage 12 of the drive spindle 10.
This unique torque transfer arrangement is preferably combined with
the torque key 28 and torque socket arrangement described directly
above to provide for direct torque transfer from the drive 105 to
the bur 50 without the possibility of any slippage and the
associated heat generation and possible thermal damage to
components of the drive arrangement, especially the tempered tool
retaining arms 24. The torque transfer arrangement includes a
locking portion 53 on the bur 50, which has an outer non-circular
cross section (see FIGS. 3D, 4A to 8, 10, 11) and a locking socket
27 in the chuck 20, which has a complementary or interlocking
cross-section. The locking portion 53 is shaped to slidably fit
into the locking socket 27 to allow length adjustment of the bur 50
by retracting the bur 50 from the fully inserted position in
accordance with the principle aspect of the invention.
[0077] Preferably, the locking socket 27 is co-extensive with the
first tool seat 14, which means the first tool seat 14 is shaped as
a locking socket of a cross-sectional shape permitting fitting and
slidable insertion of the locking portion 53 of the bur 50 while
positively preventing rotation of the locking portion 53 in the
locking socket 27. FIG. 4A shows an axial end view of a preferred
embodiment of a dental bur 50 in accordance with the present
invention having a locking portion 53 of triangular cross-section.
FIG. 8 illustrates an end view of the drive spindle 10 of the
preferred embodiment of FIG. 2, illustrating the cross-sectional
shape of the locking socket 27 which is not directly complementary
to the cross-section of the locking portion 53 shown in FIG. 4, but
nevertheless provides an interference fit of the locking portion 53
in the locking socket 27 to guarantee a reliable interlocking
between the locking portion 53 and the locking socket 27. In this
embodiment, the locking socket 27 is a multi-faceted socket formed
in a portion of the tool passage 12 of the chuck 20 near the driven
end 21 of the chuck. The multi-faceted locking socket 27 provides
multiple possible insertion orientations for the triangular lock
portion 53 to improve the chance of aligning the locking portion 53
with the locking socket 27 without the aid of visual
pre-alignment.
[0078] In a particularly preferred embodiment, the locking socket
27 extends substantially the whole length of the tool passage 12
for maintaining concentricity during rotation. It is preferable
that the locking portion 53 and the locking socket 27 be rotation
symmetrical, which means symmetrical about the axis of rotation to
prevent excessive vibration of the bur 50 or chuck 20, and thus the
handpiece, during high speed rotation. In the alternative, the
locking portion 53 and/or the locking socket 27 can also be
momentum symmetrical, which means weight balanced about the axis of
rotation, again to prevent excessive vibration in the
handpiece.
[0079] To improve the ease of proper alignment of the locking
portion 53 with the locking socket 27, a particularly preferred
embodiment of the chuck 20 includes a bur aligning member 53a (FIG.
7) near the bur insertion end of the drive spindle 10. The bur
aligning member 53a preferably corresponds in shape and orientation
with the non-circular locking socket 27, which is generally located
deep in the drive head of the handpiece. This bur aligning member
53a allows for pre-alignment of the locking portion 53 with the
locking socket 27 upon insertion of the driven portion 54 into the
drive spindle 10. The bur aligning member 53a forms part of the
tool engaging tab 25 in the embodiment shown in FIG. 6.
[0080] In an alternate preferred embodiment of the tool drive
arrangement of the invention, shown in FIG. 12, all parts perform
the same function, although the chuck 20 and ram 40 are positioned
in the spindle 10 in an axially opposite orientation to that in the
embodiment of FIG. 2. The bur 50 is inserted first into the chuck
20 and subsequently enters the axially aligned and adjacent ram 40.
In this orientation, the first tool seat 14 is formed in the ram 40
and a portion of the sleeve 30 for supporting the driven end 55 of
the tool during length adjustment, and the second tool seat 16 is
located in the chuck 20 for supporting the driven portion 54 of the
tool at a position between the driven end 55 and the working
portion 56.
[0081] In the variant illustrated in FIG. 12, drive torque is
transferred to the sleeve 30 through frictional engagement with the
spindle socket 109, for example by press-fitting the spindle 10
into the spindle socket 109. The ram 40 is securely fitted into the
spindle and engages the chuck 20 in an orientation wherein lugs 44
extending from the ram 40 toward the chuck 20 engage axial slits 26
formed in the chuck 20, similar to the embodiment shown in FIG. 2.
However, torque is transferred differently from the embodiment of
FIG. 2. For torque transfer in the embodiment of FIG. 12, as shown
in FIGS. 13B and 15, a constricted portion 30a of the casing sleeve
30 provides a locking socket 27 to prevent rotation of the locking
portion 53 bur 50 relative to the sleeve 30. The locking socket 27
can be designed in any suitable manner. For instance, as shown in
FIG. 15, the constricted portion 30a can have a non-circular
cross-section complementary to the non-circular cross-section of
the locking portion 53 of the bur 50 or, alternatively, it can
provide an interference fit to form a locking socket 27, as
described elsewhere above. The constricted portion 30a also
prevents rotation of the ram 40, specifically the lugs 44, relative
to the sleeve 30. This not only maintains the ram in the same
rotational position in the sleeve 30 at all times, but also the
chuck 20 due to the interaction between the lugs 44 of the ram 40
and the axial slits 26 in the chuck 20.
[0082] In the tool drive arrangement of FIG. 12, as shown in FIG.
13B, a tool engaging tab 25 projects from one retaining arm 24,
while the second retaining arm 24a has a relatively flattened tab
25a, which essentially acts as a pressure pad against the contact
surface 60 of the mechanical indicator 59 of the bur 50 during
operation. The pressure pad may be in the form of a flattened tab
25a, as shown, or it may simply be a retaining arm without any tab.
A single tab 25 plus pressure pad 25a arrangement, which means an
asymmetrical tab arrangement, is preferred for burs 50 which have
the mechanical retraction indicator 59 located on the locking
portion 53 of the bur 50 (see FIG. 3G). In this embodiment, the
depth of the detent 51 is asymmetrical about the circumference of
the locking portion 53 of the bur 50 due to the non-circular
cross-section of the locking portion 53 (see FIGS. 4B and 4C).
During operation, the bur 50 is oriented in the spindle 10 such
that the tab 25 engages the deeper portion of the detent 51 and the
pressure pad 25a engages the shallow portion of the detent 51 where
the surface of the bur 50 has been flattened to form the triangular
locking portion 53 (FIG. 4C). This orientation is achieved by the
specific shape of the locking socket 27 in the sleeve 30 as shown
in FIG. 15. The provision of asymmetrical tabs 25 and 25a, as in
this embodiment, is especially advantageous for tools with
three-sided non-circular locking portions. The use of asymmetrical
tabs and a shaped locking socket 27 which forces the bur 50 into
the same rotational position relative to the chuck 20 significantly
reduces wear. Use of a symmetrical chuck having identical tabs
would result in one tab always being in contact with a flattened
locking surface on the tool while the other would engage the
circular external surface of the tool shaft in the locking portion
56, resulting in wear on that external surface.
[0083] A person skilled in the art will appreciate that an
asymmetric or single-tab chuck must be counterbalanced to prevent
excessive vibration during rotation, in particular at the high
rotation speeds encountered with an air turbine handpiece. This can
be achieved by balancing the weight of the retaining arms 24 and
24a, or preferably, by balancing the overall spindle system about
the central axis for smooth rotation. For example, material can be
removed, added, or repositioned in one or more of the sleeve 30,
the chuck 20 or the ram 40, to accommodate for any difference in
weight between the two retaining arms 24 and 24a, or to balance any
other asymmetrical components of the spindle 10. In the embodiment
shown in FIGS. 13B and 15, the sleeve has been designed to
counterbalance the system due to the asymmetrical design of the
chuck. The design of the locking socket 27 is also counterbalanced
to prevent vibration during rotation.
[0084] In an alternative embodiment to FIG. 12 (not shown), the ram
is in torque-receiving communication with the drive mechanism in
the handpiece by way of a torque key 28, similar to the torque key
28 on the chuck 20 of the embodiment shown in FIG. 2. The locking
socket 27 in this alternate preferred embodiment (not shown) is
preferably located within the tool-receiving bore of the ram 40 but
may also be located in the sleeve 30, similar to the constricted
portion 30a of the sleeve 30 shown in FIG. 13B. The locking socket
27 is preferably elongated and radially supports the bur 50 to
maintain concentricity during rotation at various insertion depths
between D.sub.min and D.sub.max. The socket is preferably
complementary in shape to the non-circular cross-sectional locking
portion 53 of the bur 50, or provides an interference fit similar
to that exemplified in FIGS. 6A and 6B.
[0085] As shown in FIG. 15, the constricted portion 30 of the
sleeve 30 forming the locking socket for torque transfer to the bur
50 has an asymmetrical shape to always align the bur in the socket
in the same orientation relative to the sleeve. In particular, the
cross-sectional shape of the constricted portion 30a includes a
flat portion for engagement with a flat ended section on the
locking portion 53 of the bur 50, which flat portion is
diametrically opposite a circular portion of sufficient diameter to
fittingly engage a externally circular section of the locking
portion 53. The spacing of the diametrically opposite flat and
circular portions of the locking socket in the sleeve 30
(constricted portion 30a) is selected to be substantially equal to
the dimensions of the locking portion 53 of the bur 50 so that the
locking portion is fittingly insertable into the locking socket and
locked against rotation therein for reliable torque transfer from
the sleeve 30 to the bur 50.
[0086] Other non-circular cross-sectional locking portions and
complementary locking sockets are also contemplated, for example,
square-, rectangle-, octagonal-, diamond-, star-, and flattened
circle-shape among others. A non-circular locking portion can also
have a generally circular shape with one or more indents, notches
or axial grooves projecting radially inward into the locking
portion 53. A variant in which the locking portion 53 of the bur 50
directly engages a locking socket 27 formed in a portion of the
drive mechanism, for example a turbine, for direct torque transfer
is also contemplated.
[0087] It is contemplated that a dental tool in accordance with the
present invention can have any type of working tip for contacting a
tooth surface known in the art. Furthermore, a portion or all of
the tool may be provided with a wear resistant coating. One or more
of the components of the rotatable tool drive arrangement of the
present invention may be provided with a low friction coating, for
example the lugs 44 of the ram 40. It is contemplated that a tool
according to the present invention may further comprise an axial
channel to allow passage of air or liquid from the handpiece to a
surface of a tooth. It is also contemplated that the tool of the
invention may be a tool other than a dental bur.
[0088] The above-described embodiments of the present invention are
intended to be examples only. Alterations, modifications and
variations may be effected to the particular embodiments by those
of skill in the art without departing from the scope of the
invention, which is defined solely by the claims appended
hereto.
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